It is already known that (R)-1-(4-chloro-phenyl)-ethylamine can be prepared by reacting racemic 1-(4-chloro-phenyl)-ethylamine with (S)-(-)-N-phenylcarbamate lactic acid in the presence of ethanol, filtering off the resulting crystal sludge with suction and treating it with aqueous sodium hydroxide solution in the presence of methylene chloride (cf. EP-A 0 341 475). A disadvantage of this process is that there is a considerable amount of S-(-)-phenylcarbamate lactic acid in the mother liquor which results after the crystal sludge has been filtered off with suction, which can only be isolated from the liquor in a complex method.
Furthermore, it is already known that (S)-1-(4-chloro-phenyl)-ethylamine can be obtained by reducing the mother liquor which forms during the abovementioned process by distilling off ethanol, stirring the remaining residue with tert-butyl methyl ether or toluene, separating off the crystalline salt which separates out and distilling the mother liquor (cf, DE-A 4 039 447). However, this process is too expensive to be carried out on an industrial scale.